The microwave structure of coronal condensations and its relation to proton flares

Active regions on the Sun in the 20th solar cycle are studied with special reference to their association with proton flares based on microwave interferometric observations at Toyokawa Observatory. It has been reconfirmed that the active regions associated with intense S-component emission with a high 3-cm to 8-cm flux ratio are likely to produce proton flares. About one fourth of 259 active regions during the period investigated are found to have definite features in the spatial distribution of polarization at a wavelength of 3 cm. Active regions with one particular type of polarization pattern have a good correlation with the occurrence of proton flares.     

Helical structures around quiescent solar prominences computed from observable magnetic fields

We analyse the magnetic support of solar prominences in two-dimensional linear force-free fields. A line current is added to model a helical configuration, well suited to trap dense plasma in its bottom part. The prominence is modeled as a vertical mass-loaded current sheet in equilibrium between gravity and magnetic forces.We use a finite difference numerical technique which incorporates both vertical photospheric and horizontal prominence magnetic field measurements. The solution of this mixed boundary problem generally presents singularities at both the bottom and top of the model prominence. The removal of the singularities is achieved by superposition of solutions. Together with the line current equilibrium, these three conditions determine the amplitude of the magnetic field in the prominence, the flux below the prominence and the current intensity, for a given height of the line current. A numerical check of accuracy in the removal of singularities, is done by using known analytical solutions in the potential limit.We have investigated both bipolar and quadrupolar photospheric regions. In this mixed boundary problem the polarity of the field component orthogonal to the prominence is mainly fixed by the imposed height of the line current. For bipolar regions above (respectively below) a critical height the configuration is inverse (respectively normal). For quadrupolar regions the polarity is reversed if we refer the prominence polarity to the closest photospheric polarities. We introduce the polarity of the component parallel to the prominence axis with reference to a sheared arcade. Increasing the shear with fixed boundary conditions can increase or decrease the mass supported depending on the configuration.     

Analysis of the institutional and social responses to the eruption and the lahars of Mount Pinatubo volcano from 1991 to 1998 (Central Luzon, Philippines)

Mount Pinatubo volcano erupted in June 1991 in the main island of Luzon belonging to the Philippines archipelago. Huge economic losses and population exodus have followed. This major crisis has been relayed with other crises due to rain-fed lahars which have been supplied with eruption deposits. These lahars have occurred every year since 1991 during the rainy season. They will probably last until 2005. After a brief presentation of the Philippine official response system to disasters, this paper draws up a critical analysis of the different kinds of institutional and social responses deployed to manage the different crisis and post-crisis phases of this event. Based on three viewpoints: from population, media and other actors, this analysis attempts to point out the strengths and weaknesses of the official management system, especially by studying the efficiency and the range of the solutions taken. So, it appears that the management of the June 1991 main crisis (eruption) was a success. On the other hand, difficulties have occurred with lahars risk management. Indeed, these lahars have obliged the authorities to protect and relocate thousands of people. In spite of persistent problems, the management system (monitoring/warning/evacuation) of lahar crises improves year after year. Failures appear especially within the rehabilitation program (protection/rehousing). Many direct (lack of means, preparedness, coordination, dialog, etc.) and indirect (politico-administrative, socio-economic, cultural contexts) factors come together to lock the wheels of the institutional response system. They defer the socio-economic start of this vital northern Philippines area. This revised version was published online in July 2006 with corrections to the Cover Date.     

Coherent integration time limit of a mobile receiver for indoor GNSS applications

There is an emerging requirement for processing global navigation satellite system (GNSS) signals indoor where the signal is very weak and subjected to spatial fading. Typically, longer coherent integration intervals provide the additional processing gain required for the detection and processing of such weak signals. However, the arbitrary physical motion of the handset imputed by the user limits the effectiveness of longer coherent integration intervals due to the spatial decorrelation of the multipath-faded GNSS signal. In this paper, limits of coherent integration due to spatial decorrelation are derived and corroborated with experimental verification. A general result is that the processing gain resulting from direct coherent integration saturates after the antenna has moved through a certain distance, which for typical indoor propagation, is about half a carrier wavelength. However, a refined Doppler search coupled with a prolonged coherent integration interval extends this limit, which is effectively a manifestation of selective diversity.     

Comparative phylogeography of African rain forest trees: A review of genetic signatures of vegetation history in the Guineo-Congolian region

The biogeographic history of the African rain forests has been contentious. Phylogeography, the study of the geographic distribution of genetic lineages within species, can highlight the signatures of historical events affecting the demography and distribution of species (i.e. population fragmentation or size changes, range expansion/contraction) and, thereby, the ecosystems they belong to. The accumulation of recent data for African rain forests now enables a first biogeographic synthesis for the region. In this review, we explain which phylogeographic patterns are expected under different scenarios of past demographic change, and we give an overview of the patterns detected in African rain forest trees to discuss whether they support alternative hypotheses regarding the history of the African rain forest cover. The major genetic discontinuities in the region support the role of refugia during climatic oscillations, though not necessarily following the classically proposed scenarios. We identify in particular a genetic split between the North and the South of the Lower Guinean region. Finally we provide some perspectives for future study.     

Solar abundance of praseodymium

16 lines of Pr ii possibly present in the solar photospheric spectrum have been studied. When including hyperfine structure in synthetic calculations, investigations of 9 lines result in an abundance A _Pr = 0.71 ± 0.08 in the log A _H = 12.00 scale.     

Long-Term Evolution of the Seismic Activity Preceding the 2015 Seismic Crisis at Deception Island Volcano,Antarctica (2008-2015)

Surveys in Geophysics - Deception Island is an active volcano located in the South Shetland Islands, Antarctica. Although the last eruptions occurred in 1967-1970, the volcano has undergone periods...     

Distribution functions of spring discharges according to their lithologies and the influence of lower limit to flow: an example from Spain

Specific functions of distribution of the number of springs and of their contributions according to flow for each of nine lithological groups are established. These functions confirm the suitability of a general type of distribution (Sanz 1996), which is a borderline case of the lognormal distribution. The statistical methods proposed for the lithological types presented can be applied to any region if data on flow and lithology of the aquifers drained by springs are available. These methods have been applied to Spain, a representative region with varied geology, climate and topography; 71.2% of spring flow is supplied by limestones, 19.17% by alluvial sediments and marls, 6.7% by conglomerates and sandstones, and 3% by slates, plutonic rocks, quartzites, and other groups. Springs with discharge rates exceeding 2000 L/s exist only in limestones. The majority of springs with low flow occur in marls. If we consider springs with flow greater than 0.5 L/s, alluvial sediments, sandstones, marls, and limestones have the greatest density of springs per surface area, although the average flow varies greatly from one lithology to the next. The cumulative estimated discharge and the estimated number of springs depend upon the definition of the lower limit of flow. For example, total discharge is reduced by 30% if we eliminate all springs with flow lower than 0.5 L/min.     

Land use and disturbance effects on the dynamics of natural ecosystems of the Monte Desert: Implications for their management

The complex interactions between human activity and natural processes determine non-linear dynamics in ecosystems that can difficult their management. Human settlements in arid lands contribute to the modification of disturbance regimes, including the introduction of new disturbances and the elimination of others. In consequence, they can alter the functional mechanisms that allow systems to overcome limiting factors, leading to desertification. In this revision, we evaluated the effects of the changes on disturbance regimes produced by the different forms of land transformation on the structure and function of ecosystems of the Monte Biogeographical Province, in Argentinean arid west. Two approaches were used: the analysis of land use history and the analysis of the effects of the main disturbances on the dynamics of different communities. We concluded that throughout the history of the Monte Desert, the joint action of natural and anthropic agents has resulted in complex dynamics that lead most area of the Monte to a moderate to severe status of desertification. The modification of the disturbance regime had strong consequences for several aspects of the dynamics of communities, such as species composition and diversity, water dynamics, soil conditions, trophic structure and productivity of Monte Desert ecosystems. However, disturbance regimes could be managed to promote favorable transitions in ecosystems and, therefore, could be a tool for optimizing productivity of agro-ecosystems, and recovering and conserving natural ecosystems.